Some internal combustion engines incorporate a recirculation duct, which takes a portion of the exhaust gas circulating in an exhaust line of the engine, and reinjects it into an intake line of this engine. Exhaust gas recirculated in this way is referred to as EGR gas.
The EGR gas rate, referred to as the EGR rate, present in the gas mixture fed at a moment t into the cylinders of the engine, is a parameter used by an electronic control unit of the engine to regulate the functioning of the latter. The EGR rate at the inlet of the cylinder actually plays an important part in the quality of the combustion of the gas in the cylinders, the fuel consumption of the engine, the limitation of polluting emissions resulting from the combustion of gas, and for engine tuning in general.
The value of the EGR rate used by the electronic control unit is currently a value determined at the moment t at the outlet of the recirculation duct to the intake duct, and not at the inlet of the cylinder themselves.
Different methods are in fact known for determining this EGR rate at the outlet of the recirculation duct to the intake duct, for example by measuring the flow rate of the EGR gas and the flow rate of the fresh air mixed at this location in the intake line or by a calculation based on measured pressure and temperature values either side of a recirculation valve fitted along the path of this recirculation duct using the Barré Saint Venant formula.
However, the value of the EGR rate at the inlet of the cylinder at the moment t can be different from the value of the EGR rate at the outlet of the recirculation duct at the moment t: the value of the EGR rate taken into account by the electronic control unit is therefore not very precise.